#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <sys/stat.h>
#include <pthread.h>
#include <sys/wait.h>
#include <stdlib.h>

#define ISspace(x) isspace((int)(x))
//函数说明：检查参数c是否为空格字符，
//也就是判断是否为空格(' ')、定位字符(' \t ')、CR(' \r ')、换行(' \n ')、垂直定位字符(' \v ')或翻页(' \f ')的情况。
//返回值：若参数c 为空白字符，则返回非 0，否则返回 0。

#define SERVER_STRING "Server: tinyhttp/0.1.0\r\n"//定义server名称

//void accept_request(int);//接收请求
void *accept_request(void* client);
void bad_request(int);//无效请求
void cat(int, FILE *);
void cannot_execute(int);
void error_die(const char *);
void execute_cgi(int, const char *, const char *, const char *);
int get_line(int, char *, int);
void headers(int, const char *);
void not_found(int);
void serve_file(int, const char *);
int startup(u_short *);
void unimplemented(int);

//接收客户端的连接，并读取请求数据
void *accept_request(void* from_client)
{
	int client = *(int *)from_client;
	char buf[1024];
	int numchars;
	char method[255];
	char url[255];
	char path[512];
	size_t i, j;
	struct stat st;
	int cgi = 0;      /* becomes true if server decides this is a CGI
                    * program */
	char *query_string = NULL;
//获取一行HTTP报文数据
	numchars = get_line(client, buf, sizeof(buf));
//
	i = 0;
	j = 0;
//对于HTTP报文来说，第一行的内容即为报文的起始行，格式为<method> <request-URL> <version>，
//每个字段用空白字符相连
	while (!ISspace(buf[j]) && (i < sizeof(method) - 1)) {
//提取其中的请求方式是GET还是POST
		method[i] = buf[j];
		i++;
		j++;
	}
	method[i] = '\0';
//函数说明：strcasecmp()用来比较参数s1 和s2 字符串，比较时会自动忽略大小写的差异。
//返回值：若参数s1 和s2 字符串相同则返回0。s1 长度大于s2 长度则返回大于0 的值，s1 长度若小于s2 长度则返回小于0 的值。
	if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) {
//tinyhttp仅仅实现了GET和POST
		unimplemented(client);
		return NULL;
	}
//cgi为标志位，置1说明开启cgi解析
	if (strcasecmp(method, "POST") == 0)
//如果请求方法为POST，需要cgi解析
		cgi = 1;

	i = 0;
//将method后面的后边的空白字符略过
	while (ISspace(buf[j]) && (j < sizeof(buf)))
		j++;
//继续读取request-URL
	while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf))) {
		url[i] = buf[j];
		i++;
		j++;
	}
	url[i] = '\0';
//如果是GET请求，url可能会带有?,有查询参数
	if (strcasecmp(method, "GET") == 0) {
		query_string = url;
		while ((*query_string != '?') && (*query_string != '\0'))
			query_string++;
		if (*query_string == '?') {
			//如果带有查询参数，需要执行cgi，解析参数，设置标志位为1
			cgi = 1;
			//将解析参数截取下来
			*query_string = '\0';
			query_string++;
		}
	}
//以上已经将起始行解析完毕
//url中的路径格式化到path
	sprintf(path, "htdocs%s", url);

//如果path只是一个目录，默认设置为首页index.html
	if (path[strlen(path) - 1] == '/')
		strcat(path, "index.html");

//函数定义:    int stat(const char *file_name, struct stat *buf);
//函数说明:    通过文件名file_name获取文件信息，并保存在buf所指的结构体stat中
//返回值:     执行成功则返回0，失败返回-1，错误代码存于errno（需要include <errno.h>）
	if (stat(path, &st) == -1) {
//假如访问的网页不存在，则不断的读取剩下的请求头信息，并丢弃即可
		while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
			numchars = get_line(client, buf, sizeof(buf));
		//最后声明网页不存在
		not_found(client);
	} else {
//如果访问的网页存在则进行处理
		if ((st.st_mode & S_IFMT) == S_IFDIR)//S_IFDIR代表目录
//如果路径是个目录，那就将主页进行显示
			strcat(path, "/index.html");
		if ((st.st_mode & S_IXUSR) ||
		    (st.st_mode & S_IXGRP) ||
		    (st.st_mode & S_IXOTH)    )
			//S_IXUSR:文件所有者具可执行权限
			//S_IXGRP:用户组具可执行权限
			//S_IXOTH:其他用户具可读取权限
			cgi = 1;
		if (!cgi)
			//将静态文件返回
			serve_file(client, path);
		else
			//执行cgi动态解析
			execute_cgi(client, path, method, query_string);

	}

	close(client);//因为http是面向无连接的，所以要关闭
	return NULL;
}

//通知客户，它提出的请求有问题
void bad_request(int client)
{
	char buf[1024];
//发送400
	sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n");
	send(client, buf, sizeof(buf), 0);
	sprintf(buf, "Content-type: text/html\r\n");
	send(client, buf, sizeof(buf), 0);
	sprintf(buf, "\r\n");
	send(client, buf, sizeof(buf), 0);
	sprintf(buf, "<P>Your browser sent a bad request, ");
	send(client, buf, sizeof(buf), 0);
	sprintf(buf, "such as a POST without a Content-Length.\r\n");
	send(client, buf, sizeof(buf), 0);
}

//读取文件并发送给客户端
void cat(int client, FILE *resource)
{
//发送文件的内容
	char buf[1024];
//读取文件到buf中
	fgets(buf, sizeof(buf), resource);
	while (!feof(resource)) { //判断文件是否读取到末尾
//读取并发送文件内容
		send(client, buf, strlen(buf), 0);
		fgets(buf, sizeof(buf), resource);
	}
}

//通知客户端不能执行CGI脚本
void cannot_execute(int client)
{
	char buf[1024];
//发送500
	sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "Content-type: text/html\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "<P>Error prohibited CGI execution.\r\n");
	send(client, buf, strlen(buf), 0);
}

//打印出一个错误信息perror()并退出程序指示错误

void error_die(const char *sc)
{
	perror(sc);
	exit(1);
}

//执行cgi动态解析
void execute_cgi(int client, const char *path,
                 const char *method, const char *query_string)
{
	char buf[1024];
	int cgi_output[2];//声明的读写管道.
	int cgi_input[2];
	pid_t pid;
	int status;
	int i;
	char c;
	int numchars = 1;
	int content_length = -1;

	buf[0] = 'A';
	buf[1] = '\0';
	if (strcasecmp(method, "GET") == 0)
//如果是GET请求
//读取并且丢弃头信息
		while ((numchars > 0) && strcmp("\n", buf))
			numchars = get_line(client, buf, sizeof(buf));
	else {
//处理的请求为POST
		numchars = get_line(client, buf, sizeof(buf));
		while ((numchars > 0) && strcmp("\n", buf)) {
			//循环读取头信息找到Content-Length字段的值
			buf[15] = '\0';//目的是为了截取Content-Length:

			if (strcasecmp(buf, "Content-Length:") == 0)
				//"Content-Length: 15"
				content_length = atoi(&(buf[16]));//获取Content-Length的值
			numchars = get_line(client, buf, sizeof(buf));
		}
		if (content_length == -1) {
			//错误请求
			bad_request(client);
			return;
		}
	}
//返回正确响应码200
	sprintf(buf, "HTTP/1.0 200 OK\r\n");
	send(client, buf, strlen(buf), 0);
//建立管道，这一步很重要
	if (pipe(cgi_output) < 0) {
		cannot_execute(client);
		return;
	}
	if (pipe(cgi_input) < 0) {
		cannot_execute(client);
		return;
	}

	if ( (pid = fork()) < 0 ) {
		cannot_execute(client);
		return;
	}
//fork出一个子进程运行cgi脚本
	if (pid == 0) { /* 子进程: 运行CGI 脚本 */
		char meth_env[255];
		char query_env[255];
		char length_env[255];

		dup2(cgi_output[1], 1);//1代表着stdout，0代表着stdin，将系统标准输出重定向为cgi_output[1]
		dup2(cgi_input[0], 0);//将系统标准输入重定向为cgi_input[0]，这一点非常关键，
		//cgi程序中用的是标准输入输出进行交互
		close(cgi_output[0]);//关闭了cgi_output中的读通道
		close(cgi_input[1]);//关闭了cgi_input中的写通道
		//CGI标准需要将请求的方法存储环境变量中，然后和cgi脚本进行交互
		//存储REQUEST_METHOD
		sprintf(meth_env, "REQUEST_METHOD=%s", method);
		putenv(meth_env);
		if (strcasecmp(method, "GET") == 0) {
			//存储QUERY_STRING
			sprintf(query_env, "QUERY_STRING=%s", query_string);
			putenv(query_env);
		} else { /* POST */
			//存储CONTENT_LENGTH
			sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
			putenv(length_env);
		}
		execl(path, path, NULL);//执行CGI脚本
		exit(0);
	} else {    /* 父进程 */
		close(cgi_output[1]);//关闭了cgi_output中的写通道，注意这是父进程中cgi_output变量和子进程要区分开
		close(cgi_input[0]);//关闭了cgi_input中的读通道
		if (strcasecmp(method, "POST") == 0)
			for (i = 0; i < content_length; i++) {
				//开始读取POST中的内容
				recv(client, &c, 1, 0);
				//将数据发送给cgi脚本
				write(cgi_input[1], &c, 1);
			}
		//读取cgi脚本返回数据
		while (read(cgi_output[0], &c, 1) > 0)
			//发送给浏览器
			send(client, &c, 1, 0);
//运行结束关闭
		close(cgi_output[0]);
		close(cgi_input[1]);

		waitpid(pid, &status, 0);
	}
}


//解析一行http报文
int get_line(int sock, char *buf, int size)
{
	int i = 0;
	char c = '\0';
	int n;

	while ((i < size - 1) && (c != '\n')) {
		n = recv(sock, &c, 1, 0);
		/* DEBUG printf("%02X\n", c); */
		if (n > 0) {
			if (c == '\r') {
				n = recv(sock, &c, 1, MSG_PEEK);
				/* DEBUG printf("%02X\n", c); */
				if ((n > 0) && (c == '\n'))
					recv(sock, &c, 1, 0);
				else
					c = '\n';
			}
			buf[i] = c;
			i++;
		} else
			c = '\n';
	}
	buf[i] = '\0';

	return(i);
}

//返回关于文件的信息HTTP头文件。参数：用于在文件名上打印标题的套接字。
void headers(int client, const char *filename)
{
	char buf[1024];
	(void)filename;  /* could use filename to determine file type */
//发送HTTP头
	strcpy(buf, "HTTP/1.0 200 OK\r\n");
	send(client, buf, strlen(buf), 0);
	strcpy(buf, SERVER_STRING);
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "Content-Type: text/html\r\n");
	send(client, buf, strlen(buf), 0);
	strcpy(buf, "\r\n");
	send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Give a client a 404 not found status message. */
/**********************************************************************/
void not_found(int client)
{
	char buf[1024];
//返回404
	sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, SERVER_STRING);
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "Content-Type: text/html\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "<BODY><P>The server could not fulfill\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "your request because the resource specified\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "is unavailable or nonexistent.\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "</BODY></HTML>\r\n");
	send(client, buf, strlen(buf), 0);
}


//将请求的文件发送回浏览器客户端
void serve_file(int client, const char *filename)
{
	FILE *resource = NULL;
	int numchars = 1;
	char buf[1024];
	buf[0] = 'A';
	buf[1] = '\0';
	while ((numchars > 0) && strcmp("\n", buf)) //将HTTP请求头读取并丢弃
		numchars = get_line(client, buf, sizeof(buf));
//打开文件
	resource = fopen(filename, "r");
	if (resource == NULL)
		not_found(client);//如果文件不存在，则返回not_found
	else {
//添加HTTP头
		headers(client, filename);
//并发送文件内容
		cat(client, resource);
	}
	fclose(resource);//关闭文件句柄
}

//启动服务端
int startup(u_short *port)
{
	int httpd = 0;
	struct sockaddr_in name;
//设置http socket
	httpd = socket(PF_INET, SOCK_STREAM, 0);
	if (httpd == -1)
		error_die("socket");
	memset(&name, 0, sizeof(name));
	name.sin_family = AF_INET;
	name.sin_port = htons(*port);
	name.sin_addr.s_addr = htonl(INADDR_ANY);
//绑定端口
	if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
		error_die("bind");
	if (*port == 0) { /*动态分配一个端口 */
		socklen_t  namelen = sizeof(name);
		if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
			error_die("getsockname");
		*port = ntohs(name.sin_port);
	}
//监听连接
	if (listen(httpd, 5) < 0)
		error_die("listen");
	return(httpd);
}

//通知客户端所请求的Web方法尚未实现。
void unimplemented(int client)
{
	char buf[1024];
//发送501说明相应方法没有实现
	sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, SERVER_STRING);
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "Content-Type: text/html\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "</TITLE></HEAD>\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n");
	send(client, buf, strlen(buf), 0);
	sprintf(buf, "</BODY></HTML>\r\n");
	send(client, buf, strlen(buf), 0);
}

/**********************************************************************/

int main(void)
{
	int server_sock = -1;
	u_short port = 0;
	int client_sock = -1;
	struct sockaddr_in client_name;
	socklen_t client_name_len = sizeof(client_name);
	pthread_t newthread;
//启动server socket
	server_sock = startup(&port);

	printf("httpd running on port %d\n", port);
//简单循环模型,便于测试
	while (1) {
//接受客户端连接
		client_sock = accept(server_sock,
		                     (struct sockaddr *)&client_name,
		                     &client_name_len);
		if (client_sock == -1)
			error_die("accept");
		/*启动线程处理新的连接 */
		if (pthread_create(&newthread , NULL, accept_request, (void*)&client_sock) != 0)
			perror("pthread_create");
	}
//关闭server socket
	close(server_sock);

	return(0);
}
